We don't know because nobody is mass building any nuclear reactors right now (micro or traditional - it's one of the main reasons there's so many cost overruns with anything being built right now). There's also no mass scale example of renewable desalination, either. It's almost all bespoke, so it's mostly theoretical.
If climate change continues and water becomes something to fight over like oil was in the 20th century, then we may finally see traction on both fronts.
But there are pretty large-scale deployments of renewables and battery storage going on, so presumably some fraction of the power used in today’s desalinization plants is generated from renewables (at least in China.) At very least there should be no deep mysteries about the generation costs.
Sure, but desalination is very power hungry. In Oman they managed to get a desalination plant to be 1/3 directly covered by solar in the desert and they still need alternative power for when that 1/3 is unavailable. Battery costs are still high. If it was that easy, it would be done.
What’s technically more achievable: adapting desalinization so it can work efficiently on intermittent power, reducing battery costs, or getting SMRs up and widely deployed along the Mexican coast in the next decade? I don’t have any idea if the answer to this but I don’t think they’re all equally pie in the sky either.
In theory, SMRs - *if* they're built out at scale (meaning for many other uses). The problem is the first users are going to pay a premium and it likely won't happen until they're already scaled out (and may still have to compete with renewable subsidies).
Renewables should still be competitive in certain cases, though.
If climate change continues and water becomes something to fight over like oil was in the 20th century, then we may finally see traction on both fronts.